JP6880521B2 - Light reflective film and edge light type backlight - Google Patents

Description

The present invention relates to a light-reflecting film in which the surface roughness on both sides of the film and the bending rigidity of the film are within a specific range, so that a decrease in the uniformity of brightness in the screen can be suppressed and the reflection characteristics are also excellent. .. Further, the light reflective film of the present invention is suitably used for a backlight device for image display, a reflective sheet for a lamp reflector, a reflective sheet for lighting equipment, a reflective sheet for a lighting sign, etc., and particularly an edge light type for image display. It can be suitably used for a reflective sheet of a backlight device.

In many cases, a light-reflecting film is installed in the back light source (backlight) used for liquid crystal displays, lighting signs, etc. in order to effectively use the light energy. The rear light source is classified into a direct type and an edge light type according to the location of the light source. The direct type is a type in which the light source is arranged at the back of the screen in what is called a display, and the edge light type is used together with a light guide plate in which a light source is installed at the edge of the screen and converts light in the screen direction.

In recent years, by adopting a light emitting diode (hereinafter referred to as LED) that consumes less power and can increase the output as a light source for a rear light source, the light source can be placed on the back surface of a conventional backlight device even in a large liquid crystal display. From the method of arranging the light source, the method of arranging the light source on the side surface is adopted, which is advantageous for thinning. For the housing of such a large LED backlight, uneven processing with a height of about 5 to 10 mm is performed to improve the strength of the housing, electrical wiring and board storage, and the end of the housing close to the LED light source is used. Grooving for heat dissipation may be provided. Further, since the edge light type backlight has a structure in which the light guide plate and the reflector are in contact with each other, the light guide plate and the reflector are pressed against each other or rubbed against each other in the backlight having a non-uniform housing mechanism as described above. As a result, one of them may hurt the other, or the other may be in close contact with each other, resulting in a partially high-brightness portion (hereinafter referred to as bright spot unevenness).

In response to such a problem, Patent Documents 1 and 2 disclose a reflective sheet in which a layer containing soft beads is laminated on a base sheet layer, but it is emitted from an uneven state of a mechanism / housing or a light source. Depending on the heat or the type of light guide plate used, the effect of suppressing bright spot unevenness may not be sufficient.

Further, particularly in a large-sized liquid crystal display or the like, the light-reflecting sheet itself is bent in the groove or the like of the above-mentioned housing because of its large size, and as a result, the brightness as a backlight changes along with the bending of the light-reflecting sheet. (The deflection is visually recognized. Hereinafter referred to as uneven deflection) may occur. To solve such a problem, Patent Document 3 discloses a method of avoiding bending of the light reflecting sheet by attaching the light reflecting sheet to the housing, but there is a problem such as an increase in manufacturing cost due to an increase in the number of steps. was there.

Japanese Unexamined Patent Publication No. 2003-92018 Special Table 2008-512719 Japanese Unexamined Patent Publication No. 2010-23804

In edge light type backlights for liquid crystal displays, due to recent design changes such as larger screens, conventional light-reflecting sheets may cause damage due to contact with the light guide plate or uneven bright spots due to close contact. ..

Further, particularly in a large-screen liquid crystal display, in addition to the above-mentioned problems, there is a problem that uneven bending is visually recognized due to bending of the light reflecting sheet in a groove or the like provided in the housing.

An object of the present invention is to provide a light-reflecting film that reduces the problems of bright spot unevenness and bending unevenness and improves the uniformity of the screen of a liquid crystal display. In particular, it is an object of the present invention to provide a light reflecting film that is suitably used in an edge light type backlight device in which an LED light source is arranged on a side surface.

Light reflection film of the present invention to solve the above problems is to meet all the following items (i) ~ (v), on at least one surface, nylon, acrylic, from at least one selected from the group consisting of polystyrene and polyurethane It is coated with organic particles .

(I) A film in which at least two layers are laminated (ii) The difference between the surface roughness SRa of one surface and the other surface is 1.0 μm or more (iii) The surface roughness of the one surface The value obtained by dividing (SRa) by the surface roughness (SRa) of the other surface is 6.0 or more (iv) The thickness T (μm) of the entire film and the flexural rigidity S (mN · m) are 1 ≦ S / T x 1000 ≤ 25
Satisfy the formula of.
(V) The surface roughness (SRa) of one of the surfaces is 1.90 μm or less.

According to the present invention, it is possible to obtain a light-reflecting film having excellent screen uniformity while maintaining reflection characteristics and suppressing the occurrence of luminance unevenness including bright spot unevenness and bending unevenness when used as a backlight. Can be done. Therefore, it can be suitably used for an edge light type backlight device. In addition, since it has high rigidity and excellent brightness, it can reduce breakage and scratch marks that occur during processing and assembly, and it is suitable for use not only as a thin LED backlight device for large screens but also as a reflective sheet for all liquid crystal displays. can do.

This is an example of a schematic cross-sectional view of an edge light type backlight device incorporating the light reflecting film of the present invention.

The present inventors suppress the occurrence of brightness unevenness including bright spot unevenness and bending unevenness when the LED light source is incorporated into an edge light type backlight device arranged at the edge of the screen. As a result of diligent studies on a light-reflecting film having a high degree of screen uniformity, it has been found and investigated that a light-reflecting film having a specific configuration can solve such a problem.

The light-reflecting film of the present invention is a film in which at least two layers are laminated. The method for this lamination is not particularly limited, and can be arbitrarily selected, such as a coextrusion method, a dry or wet coating method on the base film, and the like. Further, each layer of the resin to be laminated may be made of the same resin, or different resins may be laminated.

Examples of the resin used in the present invention include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyolefin resins such as polyethylene / polypropylene and polycycloolefin, polyacrylic resins, and polycarbonate resins. Among them, polyester resin is preferably used in terms of price, availability, and the like. Further, the resins constituting each layer may be copolymerized with two or more kinds of resins, or different resins may be blended.

Further, in the resin of each layer, various additives such as a fluorescent whitening agent, a cross-linking agent, a heat-resistant stabilizer, an oxidation-resistant stabilizer, an ultraviolet absorber, an organic lubricant, and an inorganic substance are contained within a range that does not impair the effects of the present invention. Fine particles, fillers, light resistant agents, antistatic agents, nucleating agents, dyes, dispersants, coupling agents and the like may be added.

The ratio of the thicknesses to be laminated is not particularly specified, but the layer exhibiting the reflection performance is preferably 70% or more, more preferably 80% or more, and further preferably 85% or more of the total thickness. When the light-reflecting film of the present invention contains a plurality of layers, the total thickness means the total thickness of the plurality of layers.

Further, in the light-reflecting film of the present invention, the difference in surface roughness SRa between one surface and the other surface with respect to the surface roughness SRa on both sides measured by the method described later (hereinafter, may be simply referred to as the difference in surface roughness). Is 0.5 μm or more,
The value obtained by dividing the surface roughness (SRa) of one surface by the surface roughness (SRa) of the other surface (hereinafter, may be simply referred to as the ratio of surface roughness) is 6.0 or more.
Is preferable.

Since the difference in surface roughness of the light-reflecting film of the present invention is within the above range, it has an appropriate slipperiness with a light guide plate when incorporated into a backlight, and an appropriate degree with a housing without fixing with a tape or the like. It is considered that the unevenness of bright spots is less likely to occur because the adhesion is imparted. On the other hand, if the difference in surface roughness is not within the range, the light guide plate and the light reflecting film may be pressed against or rubbed, the light guide plate may damage the light reflecting film, or conversely, the light reflecting film may damage the light guide plate. It may hurt.

The difference in surface roughness is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 1.5 μm or more. There is no particular upper limit to the difference in surface roughness, but considering the uneven shape provided on the film, it is generally 100 μm or less. The surface roughness ratio is preferably 6.0 or more, more preferably 10.0 or more, and even more preferably 15.0 or more.

In the present invention, the "difference in surface roughness SRa between one surface and the other surface" means that the value of the surface having a large surface roughness SRa is subtracted from the value of the surface having a small surface roughness SRa, and "one surface". The value obtained by dividing the surface roughness (SRa) of the other surface by the surface roughness (SRa) of the other surface (ratio of surface roughness) is obtained by dividing the value of the surface having a large surface roughness value by the value of the surface having a small value. The value. The method for adjusting the surface roughness of the light-reflecting film of the present invention within such a range will be described later.

Further, the light-reflecting film of the present invention has a thickness T (μm) and a flexural rigidity S (mN · m) of the entire film of 1 ≦ S / T × 1000 ≦ 25.
It is preferable to satisfy the formula of. The method for measuring the thickness T (μm) and the flexural rigidity S (mN · m) of the entire film is as described later.

If S / T × 1000 is less than 1, the sheet may be broken during cutting or assembling, or uneven brightness (bending unevenness) may occur due to the bending of the reflective sheet due to the uneven portion of the housing. On the other hand, if S / T × 1000 exceeds 25, it may not be preferable from the viewpoint of film transportability and winding property. The value of S / T × 1000 is preferably 5 or more and 25 or less, more preferably 5 or more and 20 or less, still more preferably 7 or more and 18 or less, and particularly preferably 7 or more and 15 or less.

The method for expressing the light reflectivity of the light-reflecting film of the present invention is not particularly limited. For example, a reflective film in which a metal layer is vapor-deposited on a resin film and a large number of voids in the resin layer exhibit reflection performance. White reflective film, white reflective film that expresses reflective performance by containing particles with different refractive coefficients in the resin layer, and multiple resins with different refractive coefficients are alternately thickened with a thickness of about 100 nm to 1,000 nm. Examples thereof include a light-reflecting film that exhibits reflective performance by laminating in multiple layers while gradually changing. Further, the light reflecting film of the present invention may be a combination of a plurality of the above methods.

Among these methods, a white reflective film having a large number of voids in the resin layer is preferable in terms of manufacturing cost. Examples of the method of forming a large number of voids in the resin layer include a method of using a foaming agent and a method of creating voids by extruding a resin containing a nucleating agent and then stretching it in a uniaxial or biaxial manner. The latter method is used. Generally, it is preferably used because the number of steps is small.

Further, the light reflecting film of the present invention preferably has a relative reflectance (hereinafter, may be simply referred to as reflectance) measured by a method described later, which is 95% or more on at least one side. More preferably, it is 98% or more, and even more preferably 100% or more. If the reflectance of the light-reflecting film is less than 95%, the brightness as a backlight may be insufficient. When the light-reflecting film of the present invention is installed in the backlight, it is preferable to use the surface having the higher reflectance as the reflecting surface (toward the light source side).

Regarding the surface roughness of both sides of the light-reflecting film of the present invention
The difference in surface roughness SRa between one surface and the other surface is 0.5 μm or more.
Further, a method for setting the value obtained by dividing the surface roughness (SRa) of one surface by the surface roughness (SRa) of the other surface to 6.0 or more is not particularly specified, but for example, different resins are used for both surface layers. A method of co-extruding so that layers appear, a method of controlling surface roughness by adding additives such as different particles to the resin layers of both surface layers (including adding to only one surface layer), a method of resin film Examples thereof include a method of providing another layer by a wet or dry coating on one side, a method of thermoforming by pressing against a mold, a method of curing a resin, and the like.

Above all, in the wet coating method, the method of adding particles is preferable because it is simple, and it is more preferable that the particles are organic particles from the viewpoint of damage to the light guide plate.

As the organic particles, various kinds such as acrylic, urethane, nylon, silicone, polystyrene, polyester and polyolefin can be used. Further, among the organic particles, different monomers may be copolymerized, or a plurality of types may be mixed and used, and various additives such as a fluorescent whitening agent, a cross-linking agent, and heat resistance are used as long as the effects of the present invention are not impaired. Stabilizers, oxidation-resistant stabilizers, UV absorbers, fillers, light-resistant agents, antistatic agents, nucleating agents, dyes, coupling agents and the like may be added.

Various resins can be used as the binder resin used for immobilizing the organic particles when coating the light reflective film of the present invention containing organic particles, and various resins such as acrylic, polyurethane, polyester, polycarbonate, and polyolefin can be used. Can be used. Of the above resins, different monomers may be copolymerized, or a plurality of types may be mixed and used, and various additives such as fluorescent whitening agents, cross-linking agents, and heat-resistant stabilizers may be used as long as the effects of the present invention are not impaired. , Oxidation-resistant stabilizer, ultraviolet absorber, filler, light-resistant agent, antistatic agent, nucleating agent, dye, coupling agent and the like may be added.

The shape of the organic particles of the light-reflecting film of the present invention is not particularly specified, but it is preferably spherical in consideration of the damage property to the light guide plate. The term "sphere" here does not necessarily mean only a true sphere, but means a particle whose cross-sectional shape is surrounded by a curved surface such as a circle, an ellipse, a nearly circle, or a nearly ellipse. Further, in order to prevent the surface of the light-reflecting film from being scratched or to make the scratches on the surface of the light-reflecting film difficult to see, it is preferable to use amorphous inorganic particles and / or amorphous organic particles. Further, amorphous particles may be economically advantageous as compared to spherical particles.

Further, in the light reflecting film of the present invention, it is preferable that the volume average particle diameter of the organic particles is 5 μm or more and 50 μm or less. How to obtain the volume average particle size will be described later. If the volume average particle size is less than 5 μm, uneven brightness may occur due to sticking to the light guide plate. Further, if the volume average particle size exceeds 50 μm, it may not be preferable from the viewpoint of coatability. A more preferable range of the volume average particle diameter is 10 μm or more and 40 μm or less, and more preferably 20 μm or more and 30 μm or less. Further, a plurality of types of particles having different volume average particle diameters may be mixed and used.

In the present invention, the thickness T (μm) and the flexural rigidity S (mN · m) of the entire film are 1 ≦ S / T × 1000 ≦ 25.
In order to satisfy the above equation, it is more preferable that the configuration satisfies all of the following (1) to (4).

(1) Having a layer that does not substantially contain a cavity (hereinafter, may be abbreviated as A layer) and a layer that contains a cavity (hereinafter, may be abbreviated as B layer).

(2) The layer containing the cavity (layer B) contains a resin and inorganic particles that are incompatible with the matrix resin.

(3) When the total mass of the layer (B layer) containing the cavity is 100% by mass, the content of the resin incompatible with the matrix resin is 5% by mass or more and less than 12% by mass.

(4) When the total mass of the layer (B layer) containing the cavity is 100% by mass, the content of the inorganic particles is 15% by mass or more and less than 30% by mass.

The light-reflecting film of the present invention may be composed of the above-mentioned two layers of A layer and B layer, or may have another layer between or outside the A layer and the B layer. ..

In addition, the light-reflecting film of the present invention preferably has two or more layers other than the coating, and when the number of layers is two or more, it contains a layer (A layer) that does not substantially contain cavities and cavities. As described above, it is preferable that there are two or more layers including the layer (B layer). It should be noted that a three-layer structure of A layer / B layer / A layer is more preferable. In addition, in the layer other than the coating, for example, the adhesive layer and the other film in the case where another film is laminated via the adhesive layer are also counted as one layer.

Also, if the number of layers other than the coating is increased,
1 ≤ S / T x 1000 ≤ 25
On the other hand, if the number of layers is increased, the manufacturing process becomes complicated and a large number of materials are required, so that the manufacturing cost may increase. The upper limit of the number of layers other than the coating is preferably 5 layers or less, more preferably 4 layers or less, and further preferably 3 layers or less.

In the present invention, it is more preferable that the configuration satisfies all of the above (1) to (4) as described above. Then, by making the configuration satisfy all of the above (1) to (4), the effect of the present invention can be suitably exhibited even when the number of layers other than the coating is relatively small.

It is preferable that the B layer containing the cavity contains both a resin incompatible with the matrix resin and inorganic particles. In the present invention, the matrix resin is observed by the cross-sectional SEM observation method described later ([Measurement of physical property values and evaluation method of effect] (1) Total film thickness T, presence / absence of laminated structure, and thickness of each layer). It refers to the resin component that occupies the largest area of the cut surface excluding cavities and inorganic particles.

When a plurality of resins are copolymerized, completely blended, or the additives are uniformly dissolved in the resin, these are collectively referred to as a matrix resin. For example, when the matrix resin of the B layer is polyester, the resin incompatible with the matrix resin (hereinafter, may be abbreviated as incompatible resin) may be a homopolymer or a copolymer. Often, polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, cyclic polyolefin resins, polystyrene resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, and fluororesins are preferably used. These may be used in combination of two or more. Among the above-mentioned incompatible resins, a resin having a large critical surface tension difference from that of a polyester resin and which is not easily deformed by heat treatment after stretching is preferable. Specific examples thereof include crystalline polyolefins such as polyethylene, polypropylene, polybutene and polymethylpentene, amorphous cycloolefin-based copolymers, and copolymers thereof.

By containing the incompatible resin, a cavity having the incompatible resin as a core is created at the time of stretching, and light reflection occurs at the interface of the cavity. Therefore, in order to obtain high reflectance, this cavity may be increased. However, the increase in cavities may reduce the reflective interface due to the bonding between the cavities, and also lead to a decrease in the strength of the reflective film, so that the cavities are easily destroyed when a local force is applied to the reflective film. Therefore, when the reflective film is incorporated into the LED backlight housing for a thin and large screen, scratch marks may be formed on the reflective film due to the uneven portion of the housing or the uneven portion of the light guide plate, which may cause uneven brightness. .. An excessive increase in cavities may reduce the apparent density of the light-reflecting film and reduce the rigidity, which may be unfavorable from the viewpoint of handleability. Further, such a light-reflecting film may be broken during processing or assembling, or the reflective film may be bent due to the uneven portion of the housing, resulting in uneven brightness.

On the other hand, inorganic particles scatter light and thus improve reflectance. However, excessive addition of the inorganic particles may reduce the reflection performance due to the light absorption of the inorganic particles, reduce the effect of improving the reflectance due to the aggregation of the inorganic particles, and impair the film forming stability. Furthermore, when used in combination with an incompatible resin as in the present invention, it may inhibit the uniform formation of cavities centered on the incompatible polymer.

Therefore, in order to increase the brightness uniformity of the screen, have excellent flexural rigidity, and maintain high brightness, the light-reflecting film of the present invention ^{preferably has an apparent specific gravity of 0.6 g / cm 3} or more. More preferably, it is 0.7 g / cm ³ or more, and even more preferably 0.75 g / cm ³ or more. When the apparent specific gravity is ^{less than 0.6 g / cm 3} , the brightness is high, but the rigidity is lowered, so that uneven brightness of the reflective film due to the uneven portion of the housing may be likely to occur. The upper limit of the apparent specific gravity is not particularly limited, but is preferably ^{2.0 g / cm 3 or less in consideration of the manufacturing cost.}

In the present invention, the incompatible resin contained in the B layer is dispersed in the matrix resin with a number average particle size of 0.4 μm or more and 3.0 μm or less to obtain an appropriate number of reflective interfaces and film strength. It is preferable to obtain it, and more preferably it is in the range of 0.5 μm or more and 1.5 μm or less. The number average particle diameter referred to here is 100 incompatible resins observed by cutting out a cross section of a film and observing the cross section using a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd. It is the average value of the diameter when the area is calculated and converted into a perfect circle.

In the present invention, examples of the inorganic particles contained in the B layer include calcium carbonate, titanium dioxide, zinc oxide, zinc oxide, zinc sulfide, basic lead carbonate (white lead), barium sulfate, and the like. Therefore, calcium carbonate, barium sulfate, titanium dioxide, etc., which absorb less in the visible light region of 400 to 700 nm, are preferable from the viewpoints of reflection characteristics, concealment, manufacturing cost, and the like. In the present invention, barium sulfate and titanium dioxide are most preferable from the viewpoints of film winding property, long-term film formation stability, and improvement of reflection characteristics.

As the particle size of the inorganic particles, it is preferable to use one having a number average particle size of 0.1 μm or more and 3.0 μm or less in order to realize excellent reflectivity and concealment property, and more preferably 0.3 μm. It is 2.0 μm or less, more preferably 0.5 μm or more and 1.5 μm or less.

In the present invention, the preferable content of the incompatible resin contained in the B layer is 5% by mass or more and less than 12% by mass when the total mass of the entire layer containing the cavity (B layer) is 100% by mass. More preferably, it is 7% by mass or more and 11% by mass or less. Further, the preferable content of the inorganic particles contained in the B layer is 15% by mass or more and less than 30% by mass, more preferably 17% by mass or more and 25% by mass, when the mass of the entire B layer is 100% by mass. % Or less. By increasing the content of the incompatible resin, the number of cavities increases, so that the apparent specific gravity decreases. Further, when the content of the inorganic particles is increased, the cavities formed by the incompatible resin may be bonded to each other. The apparent specific gravity is not limited to this because it depends on the stretching conditions, but if the content of the incompatible resin and the inorganic particles contained in the B layer is within the above range, the apparent specific gravity is 0.6 g / cm ³ It is preferable that the amount is 2.0 g / cm ^{3 or less.}

In the present invention, in order to obtain a reflective film having excellent flexural rigidity and suppressing brightness unevenness caused by bending of the light reflective film, the contents of the incompatible resin and inorganic particles of the B layer should be within the above ranges. When the thickness of the A layer is TA (μm) and the thickness of the entire film is T (μm), the TA / T is more preferably 0.05 or more and 0.15 or less. More preferably, it is 0.06 or more and 0.10 or less. If the TA / T is less than 0.05, the flexural rigidity may decrease. On the other hand, when the TA / T exceeds 0.15, the loss of light energy in the A layer cannot be ignored, and the proportion of the B layer, which is the reflective layer, decreases, so that the reflection performance (luminance) may decrease.

In the present invention, the layer A is preferably a layer that does not substantially contain cavities. The term "substantially free of cavities" means a layered state in which the porosity is less than 10%. Therefore, the thickness of the layer A refers to the thickness of the layer that does not substantially contain cavities when the cross section is observed with an electron microscope. On the other hand, the thickness of the B layer refers to the thickness of the layer containing the cavity when the cross section is observed with an electron microscope. Further, when the interface is clearly observed by electron microscope observation such as when different materials are laminated, the thickness from the surface to the interface can be measured. The porosity is described later (see [Measurement of physical property values and evaluation method of effect] (1) Total film thickness T, presence / absence of laminated structure, and thickness of each layer) on the cut surface observed by the cross-sectional SEM observation method. It is defined as the ratio of the area of the voids it occupies. Specifically, it refers to a value obtained by dividing the area of the gap portion of the cross section taken at a predetermined magnification by the area of the cross section.

In the present invention, the thickness of the entire light-reflecting film is not particularly specified, but it is preferably 70 μm or more and 400 μm or less. More preferably, it is 90 μm or more and 380 μm or less. If the thickness of the entire light-reflecting film is less than 70 μm, the reflectance may be insufficient, or the flexural rigidity may be insufficient, and bending may easily occur. Further, the upper limit does not need to be particularly limited, but if it exceeds 400 μm, the reflectance cannot be expected to increase even if the thickness is made larger than this, and the manufacturing cost may increase.

[Measurement of physical property values and evaluation method of effect]
The method for evaluating the physical property value and the method for evaluating the effect of the present invention are as follows.

(1) Thickness T of the entire film, presence / absence of laminated structure, thickness of each layer, porosity The thickness T of the entire film was measured according to JIS C2151: 2006. The thickness of each layer and the presence or absence of a laminated structure were determined and calculated as follows. The light-reflecting film was cut using a microtome without being crushed in the thickness direction to obtain a section sample. The cross section of the section sample was determined by using a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd. to determine the presence or absence of a laminated structure, and the thickness of each layer was measured from imaging, and the thickness and thickness ratio of each layer were measured. Was calculated. In the measurement, in the vertical direction of the image obtained by photographing the cross section of the film with an electron microscope, the magnification is 200 to 10,000 times so that 1/2 or more of the length in the vertical direction is the length of the total thickness of the film. The image was taken with appropriate adjustment and measured. The void ratio is the area of the void portion in the obtained image obtained by imaging the cross section of the section sample with a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd. at a magnification of 2,500 times. Was divided by the area of the cross section.

(2) Surface roughness SRa
According to JIS B0602: 2001, the measurement was performed under the following conditions using a fine shape measuring machine surfcoder ET4000A manufactured by Kosaka Laboratory Co., Ltd.

-Measurement terminal: Made of diamond, tip R = 2 μm
-Measuring force: 100 μN
・ Measurement length: 1 mm
-Measurement speed: 0.1 mm / sec-Cutoff value: 0.08 mm.

(3) Apparent density A film is cut into 100 mm x 100 mm squares, and a dial gauge (No. 2109-10 manufactured by Miho Seisakusho Co., Ltd.) is attached with a stylus (No. 7002) having a diameter of 10 mm. The thickness was measured, and the average value d (μm) of the thickness was calculated. Further, this film is weighed with a direct balance, and the weight w (g) is read up to a unit ^{of 1.00 × 10 -4 g.} The value calculated by the following formula was used as the apparent density.
Apparent density = w / d × 100 (g / cm ³ ).

(4) Flexural rigidity S
The flexural rigidity was determined at a bending angle of 15 ° according to JIS P8125: 2000, and was determined using a tapered rigidity tester TELEDYNE MODEL150-D (NORTH Tonawanda, manufactured by New York USA).

(5) Relative reflectance When an integrating sphere is attached to a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies Corporation and the standard white plate (aluminum oxide) is 100%, the reflectance is the relative reflectance at a wavelength of 560 nm. Measured as. Both sides of the light-reflecting film of the present invention were measured, and the value with the higher reflectance was adopted.

(6) Identification and quantitative determination of each layer component The layers were separated by a method such as peeling. After dissolving in various solvents and aqueous solutions, the solution and precipitate were separated by filtration, and identified and quantified by analysis such as NMR, IR, EDX, fluorescent X-ray method, and ICP emission analysis method. The composition of organic particles was analyzed by identifying and quantifying them by IR.

(7) Evaluation of Relative Brightness / Bright Spot Unevenness and Flexibility Unevenness A 40-inch LCD TV (PAVV UN40B7000WF manufactured by Samsung) was disassembled, and an edge light type backlight using an LED as a light source was taken out. The size of the light emitting surface of the backlight was 89.0 cm × 50.2 cm, and the diagonal length was 102.2 cm. Further, three optical films, a light guide plate (acrylic plate, 4 mm thickness, convex portion 15 μm) and a reflective film were taken out from the backlight and cut into the same shape and size as the reflective film on which the light reflective film of the present invention was mounted. .. Instead of the mounted reflective film, the reflective films of each of the examples and comparative examples were installed so that the surface with the large surface roughness SRa faced the light guide plate side, and the light guide plate and the three optical films were separated from each other before disassembly. Installed in the same order and orientation.

Regarding the relative brightness, a white reflective film "Lumirror" (registered trademark) # 250E6SL (manufactured by Toray Industries, Inc.) was used as a reference sample (100%) using a two-dimensional color luminance meter CA-2000W manufactured by Konica Minolta Optics Co., Ltd. And evaluated according to the following criteria.

A: 103% or more B: 102% or more and less than 103% C: 101% or more and less than 102% D: less than 101%

On the other hand, regarding the uneven brightness, what can be visually recognized as the uneven brightness in front view and oblique view under a lighting environment of 500 lp or a dark place environment is observed, and the light reflection sheet and the light guide plate are brought into close contact with each other and the light guide plate is damaged. The "bright spot unevenness" (where the high-luminance portion is observed as dots) and the "bending unevenness" (brightness and darkness are observed in a wavy shape) due to the bending of the light-reflecting sheet were evaluated as follows.

[Bright spot unevenness]
A: Excellent (In a dark environment, uneven bright spots are not visible from both front and oblique viewing angles.)
B: Good (In a dark environment, uneven bright spots are not visible in front view, but are visible in oblique view.)
C: Relatively good (Under a 500 lux lighting environment, uneven bright spots are not visible from either front or oblique viewing angles, but uneven bright spots are visible in a dark environment.)
D: Slightly inferior (Under a 500 lux lighting environment, uneven bright spots are not visible in front view, but are visible in oblique view).
E: Inferior (In a 500 lpx lighting environment, the bright spot unevenness is visible from both front and oblique viewing angles.)
F: Very inferior (Very strong bright spot unevenness is visible under a lighting environment of 500 lp.)

[Flexibility]
A: Excellent (Uneven bending is not visible from both front and diagonal viewing angles in a dark environment.)
B: Good (In a dark environment, uneven bending is not visible in the front view, but is visible in the oblique view.)
C: Relatively good (Under the lighting environment of 500 lp, uneven bending is not visible from both front and oblique viewing angles, but uneven bending is visible in a dark environment).
D: Slightly inferior (Under a 500 lux lighting environment, uneven bending is not visible in the front view, but is visible in the oblique view).
E: Inferior (Under bending unevenness is visible from both front and oblique viewing angles under a lighting environment of 500 lp.)
F: Very inferior (very strong uneven bending is visible in a lighting environment of 500 lp).

(8) Volume average particle size of particles in the coating layer The volume average particle size of the particles in the coating layer (hereinafter, also referred to as coating) was determined by the following procedure.

The surface of the sample was immersed in an organic solvent, the coating layer was peeled and collected, and then the particles were removed from the coating layer by pressure bonding and sliding on a slide glass.

The volume average particle size of the collected particles is the volume of the particles when they pass through the pores using Coulter Multisizer III (manufactured by Beckman Coulter Co., Ltd.) as a particle size distribution measuring device using the pore electrical resistance method. It was measured by measuring the electric resistance of the electrolytic solution corresponding to. First, a very small amount of sample was dispersed in a dilute aqueous surfactant solution in a container. Then, a special electrolytic solution was added to the container. After that, the volume particle size was continuously measured and automatically calculated until the number of passing particles reached 100,000, and the volume average particle size was obtained.

The present invention will be described with reference to examples.

[Example 1 (reference example) ]
Using polyethylene glycol with a number average molecular weight of 4,000, the color tone of polyethylene terephthalate after polymerization (JIS K7105: 1981, measured by the stimulation value direct reading method) is L value 62.8, b value 0.5, haze 0.2. Using polyethylene terephthalate in%, 85 parts by mass of polyethylene terephthalate and 15 parts by mass of polymethylpentene were adjusted and mixed, dried at 180 ° C. for 3 hours, and then supplied to extruder B heated to 280 ° C. (layer B). )did.

On the other hand, 63 parts by mass of polyethylene terephthalate, 83 parts by mass of silicon dioxide particles polyethylene terephthalate master (containing 6% by mass of silicon dioxide with respect to the total amount of master chips) having a number average particle size of 3.5 μm, and 18 mol% of isophthalic acid in polyethylene terephthalate. The copolymerized product (PET / I) was vacuum-dried at 180 ° C. for 3 hours with 17 parts by mass, and then supplied to the extruder A heated to 280 ° C. (layer A).

Similarly, 70 parts by mass of polyethylene terephthalate, 20 parts by mass of PET / I, and 10 parts by mass of barium sulfate are adjusted and mixed, dried at 180 ° C. for 3 hours, and then supplied to extruder C heated to 280 ° C. (C layer). )did.

These polymers were laminated through a laminating device so as to form an A layer / B layer / C layer, and formed into a sheet from a T die. Further, the unstretched film obtained by cooling and solidifying this sheet with a cooling drum having a surface temperature of 25 ° C. was led to a roll group heated to 85 to 98 ° C., vertically stretched 3.6 times in the longitudinal direction, and cooled by the roll group at 21 ° C. .. Subsequently, both ends of the vertically stretched film were gripped by clips and guided to a tenter, and stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Then, the film was heat-fixed at 200 ° C. in a tenter, slowly cooled uniformly, and then cooled to room temperature to obtain a biaxially stretched laminated film. The physical characteristics of the light-reflecting film are as shown in Table 1.

[Example 2 (Reference example) ]
85 parts by mass of polyethylene terephthalate and 15 parts by mass of polymethylpentene were adjusted and mixed, dried at 180 ° C. for 3 hours, and then supplied to extruder B heated to 280 ° C. (layer B). On the other hand, 63 parts by mass of polyethylene terephthalate, 17 parts by mass of silicon dioxide particle polyethylene terephthalate master (containing 6% by mass of silicon dioxide with respect to the total amount of master chips) having a number average particle size of 3.5 μm, and 20 parts by mass of PET / I are 180 parts by mass. After vacuum drying at ° C. for 3 hours, the mixture was supplied to extruder A heated to 280 ° C. (layer A).

These polymers are laminated through a laminating device so as to form an A layer / B layer / A layer, formed into a sheet from a T die, biaxially stretched in the same manner as in Example 1, and an uncoated white sheet (A) is obtained. Obtained.

Apart from the above, 180 parts by mass of polyethylene terephthalate and 1.5 parts by mass of silicon dioxide particles polyethylene terephthalate master having a number average particle size of 3.5 μm (containing 6% by mass of silicon dioxide with respect to the total amount of master chips). After vacuum drying at ° C. for 3 hours, the mixture was supplied to an extruder heated to 280 ° C., molded into a sheet from a T die, and biaxially stretched in the same manner to obtain a transparent sheet (a).

Next, "Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution having a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 67.5 parts by mass, ethyl acetate: 29.5 parts by mass, And silicon dioxide particles (“Cyrosfair” (registered trademark) C1504 manufactured by Fuji Silysia Chemical Ltd., volume average particle size 4.0 μm): 3 parts by mass were added with stirring to prepare a coating liquid. This coating liquid was applied to one side of the white sheet (a) using Metabar # 16, and a coating layer was provided under drying conditions of 120 ° C. for 1 minute. Subsequently, a commercially available base material-less type adhesive sheet having a thickness of 25 μm is attached to the surface opposite to the surface on which the coating layer is provided, and then the sheet (a) is attached to the light-reflecting film. Got

[Example 3 (Reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 60 parts by mass, ethyl acetate: 34 parts by mass, and silicone particles (Nippon Glass) "Tospearl" (registered trademark) 145 manufactured by Sangyo Co., Ltd., volume average particle size 4.5 μm): A coating solution prepared by adding 6 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Example 4 (Reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 45 parts by mass, ethyl acetate: 43 parts by mass, and polystyrene resin particles (Sekisui) "TECHPOLYMER" (registered trademark) SBX-8 manufactured by Kaseihin Kogyo Co., Ltd., volume average particle size 4.5 μm): A coating solution prepared by adding 12 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Example 5 (reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 45 parts by mass, ethyl acetate: 43 parts by mass, and acrylic resin particles (Sekisui) "TECHPOLYMER" (registered trademark) MBX-5 manufactured by Kaseihin Kogyo Co., Ltd., volume average particle size 4.5 μm): A coating solution prepared by adding 12 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Example 6 (Reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 45 parts by mass, ethyl acetate: 43 parts by mass, and acrylic resin particles (Sekisui) "TECHPOLYMER" (registered trademark) MBX-40 manufactured by Kaseihin Kogyo Co., Ltd., volume average particle size 40 μm): A coating solution prepared by adding 12 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Example 7 (Reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 45 parts by mass, ethyl acetate: 43 parts by mass, and urethane resin particles (root) "Art Pearl" (registered trademark) C-400 transparent, volume average particle size 15 μm) manufactured by Kogyo Co., Ltd .: A coating solution prepared by adding 12 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Example 8 (reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 45 parts by mass, ethyl acetate: 43 parts by mass, and nylon resin particles (Toray) SP-10 manufactured by Co., Ltd., volume average particle size 10 μm): A coating liquid prepared by adding 12 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Example 9 (reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 45 parts by mass, ethyl acetate: 43 parts by mass, and nylon resin particles (Toray) SP-20 manufactured by Co., Ltd., volume average particle size 30 μm): A coating liquid prepared by adding 12 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Example 10 (reference example) ]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40% by mass, manufactured by Nippon Catalyst Co., Ltd.): 45 parts by mass, ethyl acetate: 43 parts by mass, nylon resin particles (Toray (Toray) SP-20 manufactured by Sekisui Chemical Co., Ltd., volume average particle size 30 μm): 9 parts by mass, and acrylic resin particles (“TECHPOLYMER” (registered trademark) MBX-5 manufactured by Sekisui Kasei Kogyo Co., Ltd., volume average particle size 5 μm): 3 A coating solution prepared by adding the parts by mass while stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film.

[Examples 22, 29 to 30 (reference examples), Examples 11 to 21, 23 to 28]
The raw material composition, thickness, and total film thickness of each layer were changed as shown in Tables 2 and 3 to prepare an uncoated white sheet. The same coating as in Example 8 was carried out to obtain a light-reflecting film.

[Comparative Examples 1 and 2]
An uncoated white sheet was obtained in the same manner as in Example 2 except that the raw material composition was changed as shown in Table 4. This was used as a light-reflecting sheet, but since the difference in surface roughness on both sides was 0.00 μm, uneven bright spots and uneven bending were visually recognized, and it could not be used for a backlight.

[Comparative Example 3]
"Hals Hybrid" (registered trademark) UV-G720T (acrylic copolymer, 40% by mass solution, manufactured by Nippon Catalyst Co., Ltd.): 70 parts by mass, ethyl acetate: 28 parts by mass, and silicon dioxide particles (Fuji) "Cyrosforbic" (registered trademark) 100 manufactured by Silysia Chemical Ltd., volume average particle size 3.0 μm): A coating solution prepared by adding 2 parts by mass with stirring was prepared. This coating liquid was applied to one side of the white sheet (a) of Example 2 using Metabar # 16, and a coating layer was provided at 120 ° C. for 1 minute to obtain a light-reflecting film. Since the difference and ratio of the surface roughness on both sides were not sufficient, uneven bright spots and uneven bending were visually recognized, and it could not be used for a backlight.

[Comparative Example 4]
The raw material composition, thickness, and total film thickness of each layer were changed as shown in Table 4 to prepare an uncoated white sheet. A light-reflecting film was obtained by applying the same coating as in Example 8, but the value of S / T × 1000 was insufficient, uneven bending was noticeably recognized, and the film could not be used for a backlight.

Here, the abbreviations in Tables 1 to 4 represent the following contents. That is,
PET: Polyethylene terephthalate,
PET / I: 15 mol% copolymerization of isophthalic acid with polyethylene terephthalate,
PET / CHDM: Polyethylene-1,4-cyclohexylene dimethylene terephthalate (polyethylene terephthalate copolymer in which 33 mol% of 1,4-cyclohexanedimethanol is copolymerized with ethylene glycol),
PBT / PTMG: Polyester ether elastomer Butylene / poly (alkylene ether) phthalate (copolymer of alkylene glycol in 30 mol% with respect to butylene terephthalate) (trade name: "Hytrel" (registered trademark) manufactured by Toray Dupont Co., Ltd.),
Silicon dioxide: Silicon dioxide with a number average particle size of 3.5 μm Titanium dioxide: Rutile-type titanium oxide with a number average particle size of 0.25 μm Barium sulfate: Barium sulfate with a number average particle size of 1.4 μm.

The light-reflecting film of the present invention can be suitably used as a reflector for an edge light type backlight, and can also be suitably used as a reflector for various backlights and a reflector for a lighting device.

1: Light reflection film 2: Light source (LED)
3: Light guide plate 4: Optical sheet 5: Housing

Claims (3)

All of the following (i) to ( vi ) and (1) to (4) are satisfied, and at least one surface contains organic particles consisting of at least one selected from the group consisting of nylon, acrylic, polystyrene and urethane. Light-reflecting film with a coating.
(I) A film in which at least two layers are laminated.
(Ii) The difference in surface roughness SRa between one surface and the other surface is 1.0 μm or more.
(Iii) The value obtained by dividing the surface roughness (SRa) of one surface by the surface roughness (SRa) of the other surface is 6.0 or more.
(Iv) The thickness T (μm) and flexural rigidity S (mN · m) of the entire film
7.2 ≤ S / T x 1000 ≤ 9.6
Satisfy the formula of.
(V) The surface roughness (SRa) of one of the surfaces is 1.90 μm or less.
(Vi) The thickness T of the entire film is 70 μm or more and 240 μm or less.
(1) Having a layer that does not substantially contain a cavity and a layer that contains a cavity.
(2) The layer containing the cavity contains a resin and inorganic particles that are incompatible with the matrix resin.
(3) When the mass of the entire layer containing the cavity is 100% by mass, the content of the resin incompatible with the matrix resin is 5% by mass or more and less than 12% by mass.
(4) When the mass of the entire layer containing the cavity is 100% by mass, the content of the inorganic particles is 15% by mass or more and less than 30% by mass. The light-reflecting film according to claim 1, wherein the volume average particle diameter of the organic particles is 5 μm or more and 50 μm or less. An edge light type backlight equipped with the light reflecting film of claim 1 or 2.

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